Electric discharge tube



A rl 17, 1962 o. REIFENSCHWEILER ETAL 3,030,157

ELECTRIC DISCHARGE TUBE Filed Feb. 28, 1958 3 ShetS-Sheet INVENTOR OTTO REIFENSCHWEILER MARTINUS HENDRIKUS MARIA SCHENKEL AARS BYWw AGENT April 17, 1962 o. REIFENSCHWEILER ETAL 3,030,167

ELECTRIC DISCHARGE TUBE Filed Feb. 28, 1958 3 Sheets-Sheet 2 INVENTOR OTTO REIFENSCHWEILER MARTINUS HENDRIKUS MARlA SCHENKELAARS BY Aprl 17, 1962 o. REIFENSCHWEILER ETAL &

ELECTRIC DISCHARGE TUBE 3 Sheets-Sheet 3 Filed Feb. 28, 1958 INVENTOR OTTO REIFENSCHWEILER MARTINUS HENDRIKUS MAR IA scH ENKELAARS GENT v 3,030,l67 EEJECTRIC DECHARGE TUBE Otto Reltensehweter and Martinus Hendrikus Maria Sehenhelaars, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, NY., a corporation of Delaware Filed Feb. 28, 1958, Ser. No. 718 253 Claims priority, application Netherlands Mar. 13, 1957 6 Claims. (Ci. 316-8) This invention relates to electric discharge tubes containing an amount of tritium. This invention also relates to methods of introducing tritium in such tubes.

lt is known to use tritium in glow -discharge tubes in order to eliminate ignition delays owing to the absence of charge carriers. The tritium may be added to the gasfilling, but this method has a limitation in that the tritium s absorbed at the glass Wall of the tube, so that it is comparatively remote from the discharge path and consequently provides only a small contribution to the production of charge carriers.

In some cases the tritium is fixed in the electrodes or at the tube wall by means of an electrodeless discharge. This requires a high pressure and a comparatively large propo'tion of the tritium must be removed by pumping.

The said two methods of introducing the tritium suifer from the disadvantage that they can hardly be carried out in a system using a rotary pump since in this case the whole system is poisoned by tritium. This contarnination is undesirable and inadmissible from the point of View of radiation hygiene. Although tritium, which produces soft beta-rays, is harmless when it is enclosed in a glass or metal envelope, any tritium which may be absorbed by the human body is harmful.

lt is also known to introduce tritium into a discharge tube either by vaporizing either a zirconium or tantalum Wire saturated with tritium or a layer deposited from vapour on a plate, or by heating a nickel tube filled With tritium; Both methods suiter from the disadvantage that they are comparatively expensive and furthermore, in these methods also the tritium is not located as closely as possible to the discharge path. It has been found that these disadvantages hamper the use of tritium. It is an object of the present invention to provide a method of using tritium which is less dangerous and not unduly eX- pensive.

According to the present invention, in an electric discharge tube containing an amount of tritium, the tritium is provided in a thin layer of titanium, zirconium or a similar hydrogen absorber, which layer consists of fine grains and is applied by sintering.

The Construction in accordance with the invention enables the fine metal powder in which the tritium is absorbed to be disposed with the aid of a binder on a metal or insulating part of the tube in close proximity to the discharge part and to be Secured thereto by sintering.

Preferably the metal grains do not exceed about 1 mircon, whilst the over-all thickness of the layer should not greatly exceed this size, since the penetrating power of the soft beta-rays of tritium is only small so that thicker layers mean an unnecessary use of the comparatively expensive tritium.

The fine metal powder may be obtained by washing out the powder which also contains larger particles with the aid of a liquid. Alte'natively, the hydride concerned, which is Very brittle, may be pulverized, if required washed out, degassed and then treated with tritium.

However, a very advantageous method of producing metal powder treated with tritium consists in atomizing the metal in a discharge in a rare-gas atmosphere, the metal powder being partly saturated with tritium during nite tates Patent or after the discharge. When the metal is atomized, the rare gas atmosphere is removed by pumpng and the tritium is introduced into the atomization space. Alternatively, the tritium may be added to the rare-gas atmosphere during the atomizing process. The powder is collected in air and worked into a paste. Instead of an atomizing process use may alternatively be made of a vaporizing process.

The metal powder should be saturated only to an extent such that in the treatment of the tube on the pump no tritium is liberated from the metal powder owing to the high temperature used, and this tritium evolution is pre- Vented by the fact that the metal powder has been exposed to air so that the outer grain layers have become iractive with respect to tritium. This means that the titanium should have a degree of saturation of about 0.3 cure per mg. of titanium for a treating temperature of about 400 C., which temperature may, if required, be maintained for three hours, that is to say, for a materially longer period than will be used in pumping. With respect to zirconium, the degree of saturation should be 0.15 cure per mg. of Zr for a treating temperature of 350 C. Instead of exposing the powder to air, an active gas may be introduced into the atomization space. Under certain conditions the inactivation is produced by the sole contact with the liquid binder.

In order that the invention may readily be carried out, it will now be described more fully, by way of example, with reference to the accompanying drawings, in which FIGS. 1 and 2 each show a discharge tube containing tritium, and

FIG. 3 shows a system for producing tritium-saturated metal powder.

In FIG. 1 reference numeral 1 denotes a glass envelope of a tube which is provided With pins 2 in its base. A cathode 3 comprises a fiat molybdenum plate having flanged edges. An anode 4 comprises a graphite block which is screwed on the anode supply lead. This lead is coated with glass 5 which extends close to the anode. An anode screening sleeve 6 is sealed to this glass coating without voids. An ignition electrode 7 extends close to the lower edge of the cathode. To the surface of the screening sleeve 6 facing the cathode there is applied a layer 8 of powdered titanium which is treated with tritium. The electrons which are emitted by the layer 3 and have an energy of at the most 20 kv. with a maximum at about 5 kv., provide an ionisation of the gas filling such that on the application of a pulse voltage to the ignition electrode 7 an auxiliary discharge is produced between this electrode and the cathode with a time delay of less than ,u. sec. This auxiliary discharge initiates the main discharge.

In FIG. 2, the tube Wall is designated 9, a disc-shaped cathode 10 being provided with a sharp projection 11, while a strip-shaped auxiliary anode 12 is arranged in close proximity to the projection 11. An auxiliary cathode 14 is arranged behind an anode 13, and in the operation of the tube there fiows between these two electrodes a current of about lO HA in order to avoid ignition delays in the main discharge path. Centrally of the tube base there is provided a layer 15 consisting of powdered zirconium which is treated with tritium. The radiation emitted by this layer should reduce the ignition delay of the auxiliary discharge path to about 0.1 sec.

In FIG. 3, reference numeral 16 denotes a glass discharge space in which a helically coiled titanium wire 17 is supported by nickel supply leads. Through a cooler 18 and a cock 19 the discharge space is connected to a vacuum pump. On one side of the discharge vessel 16 there are arranged a number of vessels 20 which are sealed by breaking seals 21 associated with a puncturing ball 22.

Each vessel 20 contains a zirconium plate 23 which is saturated with tritum. Alternatively the vessels 29 may be filled with gaseous tritum. On the other side of the discharge vessel 16 there are arranged a number of vessels which each contains a determined amount of argon and are scaled by means of breaking seals 24. The space 16 is degassed and, if required, calcined and subsequently filled through a breaking seal 24 With argon under a pressure of cms. from one of the vcssels. The wire 17 is vaporized by the passage of current so that a black spongy titanium layer is produced on the inner wall of the space 16. When a suflicient amount of titanium has been vaporized, one of the breaking seals 21 is opened and either the tritum contained in the zirconium plate is driven off by heating or the gaseous tritum contained in the vessel is admitted into the space 15. Owing to the high activity of the atomized metal layer the tritum is completely absorbed therein which `absorption may be promoted by heating to a comparatively low temperature. Alternativcly, the tritum may be provided in the discharge path at the same time as the argon. When the titanium layer has been treated with tritum, the discharge vessel 16 is cut off from the system 25 so that the layer of vaporized metal is exposed to air and the metal powder which is not entirely saturatcd with tritum becomes inactive. Subsequently, the space 16 is washed by means of a liquid, butylacetate, in which subsequently nitrocellulose is dissolved. The suspension obtained can be provided at the required points in the discharge tubes without any further treatment. 'Since the titarium is now contained in a liquid, its manipulation is not dangerous and may even be performed by machine.

Since the metal powder which is partly saturated with tritum has been exposed to air and consequently has become inactive, no tritum is evolved during the heat treatment on the pump, so that the pump system is not contaminated by radio-active material. In addition there is no waste of tritum.

A further advantage consists in that the activity of the applied suspension can immediately be measured by means of a Geiger-Miller counter or a scintillation counter.

What is claimed is:`

l. A method of introducing tritum into an electric discharge tube comprising an envelopc enclosing a discharge path which comprises the steps, depositing a thin layer of a fine-grained metal selected from the group consisting of titanium and zirconium on the wall of a vessel filled with an inert gas, introducing tritum into said vessel until said metal absorbs an amount of tritum which upon subsequent exposure to a non-inert gas rendcrs the tritumcontaining metal inactive, removing the tritum-containing metal layer from the wall of said vessel, transferring the tritum-containing metal in a finely divided state to the electric discharge tube, forming a layer of tritum-containing metal in the discharge tube in proximity to the discharge path, and subsequently heating said tritum-containing metal layer in said electric discharge tube to secure the metal layer to a surface portion within the envelope.

2. A method of introducing tritum into an electric discharge tube as claimed in claim l in which the metal is deposited in the vessel by vaporization.

3. A method of ntroducing tritum into an electric discharge tube as claimed in claim 1 in which the metal is deposited in the vessel by atomization.

4. A method of introducing tritum into an electric discharge tube as claimed in claim 1 in which the vessel is filled with inert gas when the tritum is introduced theren.

5. A method of introducing tritum into an electric discharge tube as claimed in claim 1 in which the vessel is filled with argon.

6. A method of introducing tritum into an electric discharge tube as claimed in claim 1 in which the tritumcontaining layer in the vessel is dissolved in an Organic liquid to form a suspension which is subsequently introduced into the electric discharge tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,953,781 Simon Apr. 3, 1934 2,137,198 Smith Nov. 15, 1938 2,373,175 Depp Apr. 10, 1945 2,497,911 Relly Feb. 21, 1950 2,860,269 Jefferson Nov. ll, 1958 

1. A METHOD OF INTRODUCING TRITIUM INTO AN ELECTRIC DISCHARGE TUBE COMPRISING AN ENVELOPE ENCLOSING A DISCHARGE PATH WHICH COMPRISES THE STEPS, DEPOSITING A THIN LAYER OF A FINE-GRAINED METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM ON THE WALL OF A VESSEL FILLED WITH AN INERT GAS, INTRODUCING TRITIUM INTO SAID VESSEL UNTIL SAID METAL ABSORBS AN AMOUNT OF TRITHIUM WHICH UPON SUBSEQUENT EXPOSURE TO A NON-INET GAS RENDERS THE TRITIUMCONTAINING METAL INACTIVE, REMOVING THE TRITIUM-CONTAINING METAL LAYER FROM THE WALL OF SAID VESSEL, TRANSFERRING THE TRITIUM-CONTAINING METAL IN A FINELY DIVIDED STATE TO THE ELECTRIC DISCHARGE TUBE, FORMING A LAYER OF TRITIUM-CONTAINING METAL IN THE DISCHARGE TUBE IN PROXIMITY TO THE DISCHARGE PATH, AND SUBSEQUENTLY HEATING SAID TRITIUM-CONTAINING METAL LAYER IN SAID ELECTRIC DISCHARGE TUBE TO SE- 